Head load/unload has been used primarily for portable magnetic disk products which have been concerned about the potential for "head slap", which may be caused by external shock, e.g., when the computer for housing the disk drive or the disk drive is bumped or dropped. As the result of the external shock, the head slider momentarily lifts from the rest position on the disk and bounces back down on to the surface of the disk. The impact of the head slider on the disk can cause permanent deformation in localized areas of the disk where the slider edge or corner hits the disk, also referred to as "disk rings".
Portable disk drives are normally low capacity, low performance disk drives, having low disk spindle speeds (3600 to 4500 rpm), small disks (2.5" or 1.8" form factors) and a small number of disks (1 to 3). Such disk drives are not troubled by disk flutter due to airflow turbulence because of the lower spindle speeds and smaller diameter disks.
High end disk drives are having difficulty meeting the conflicting requirements of slider start/stop durability and stiction as fly heights necessarily are reduced to accommodate the need for increased data recording density. Head slider load/unload is one method for relieving these problems. Thus, head load/unload may become widely used in the industry to enable increased recording density with reliable start/stop.
High end disk drives are typically high capacity and high performance. Such drives comprise many large diameter disks (3.5" or 5.25" form factors) and operate at very high spindle speeds (7,200 to 10,000 rpm and higher in the future). "Disk flutter" becomes a significant problem at these high spindle speeds with large disks. Disk flutter is the term for aerodynamically excited disk vibration. Air turbulence in and around the disk stack is broad band in frequency content and excites the disk structural resonances.
Shrouding appears to reduce such air turbulence when located close to the outside diameter (OD) of the disk. However, such shrouding is in direct opposition to basic head load/unload cam designs. Typical load/unload cam designs need to be positioned near the disk OD and require an area free of any shrouding. The load/unload cams also protrude into the disk stack at the OD. Thus, not only does use of typical load/unload cams prevent maximum shrouding, the protrusion into the disk stack at the OD causes increased airflow disturbance that can cause increased disk flutter.